SE0950646A1 - Method and system for operating an electric machine in a hybrid vehicle - Google Patents

Abstract

The invention comprises a system and a method for controlling an electric machine in a hybrid vehicle whose driveline comprises an internal combustion engine and a battery connected to said sub-machine, the system comprising: a tilt unit for determining the inclination of the road while driving the vehicle and generating a tilt signal therewith. , a single charge device for determining the state of charge of the battery (SOC) and generating an SOC signal depending thereon; a controller adapted to use the slope signal and the SOC signal as input signals to calculate a weighting factor and generate a weighting signal ß depending thereon; a torque unit adapted to determine a desired torque of the driver, and to generate a torque signal M depending thereon; a control unit which is adapted to calculate a control signal for the electric machine based on the weighting signal ß and the torque signal M, the electric machine being controlled according to the control signal. (Figure 4)

Description

2 energy to an electric motor that drives the vehicle. When large quantities of energy are needed, the electric motor takes energy from both the battery and the generator. The internal combustion engine is thus not integrated in the car's drive system, but the propulsion of the car takes place entirely with the help of the electric motor. In parallel hybrid vehicles, the internal combustion engine and an electric machine, which are used both as a generator and an engine, are mechanically connected via an engine shaft. An example of a parallel hybrid system is shown in Figure 2. The coupling can be placed between the internal combustion engine and the electric machine, which makes it possible to drive the vehicle only electrically. Since the internal combustion engine and the electric machine rotate at exactly the same speed (when the clutch is switched on), they complement each other and can work in parallel. Series-parallel hybrid systems are common in passenger car technology, but are usually too complicated for heavier vehicles.

The latest addition to the hybrid vehicle, charging hybrid (also cord hybrid or plug-in hybrid), is adapted for charging from the mains when the vehicle is parked. Charging hybrids have larger electric motors and powerful battery packs that in a few hours are fully charged via a cord from a standard electrical socket.

Patent application US 2005/0274553 describes a predictive energy management system for electric hybrid vehicles. The system uses various types of information such as current position and 3D maps, and generates optimal engine instructions based on the minimization of a cost function that is limited by restrictions on a battery.

Patent application DE 100 35 027 describes a method for controlling the operating condition of a hybrid vehicle. Among other things, a road profile is used to determine the various conditions.

Patent application US 2005/0274553 describes a predictive energy management system for a hybrid vehicle. By using a predictive control strategy, engine commands can be generated that optimize the operation of the hybrid vehicle now and in the future.

However, the control strategy used is complex and relatively much computational capacity is used. The object of the invention is to provide an improved way of reducing the energy consumption of a hybrid vehicle.

Summary of the invention The object described above is achieved by an aspect of the invention through a system for controlling an electric machine in a hybrid vehicle whose driveline comprises an internal combustion engine and a battery connected to said electric machine. The system comprises: - a tilt unit for determining the slope of the road when driving the vehicle and generating a tilt signal depending thereon, -a charge unit for determining the state of charge of the battery (SOC) and generating an SOC signal depending thereon; a controller adapted to use the slope signal and the SOC signal as input signals to calculate a weighting factor and generate a weighting signal ß depending thereon; a torque unit adapted to determine a desired torque of the driver, and to generate a torque signal M depending thereon; a control unit which is adapted to calculate a control signal for the electric machine based on the weighting signal ß and the torque signal M, the electric machine being controlled according to the control signal.

The object is achieved by another aspect by a method for controlling an electric machine in a hybrid vehicle whose driveline comprises an internal combustion engine and a battery connected to said electric machine. The method comprises: A) determining the slope of the road ot when driving the vehicle, B) determining the state of charge of the battery (SOC); C) use the slope of the road and the SOC of the battery as input signals to a controller to calculate a weighting factor; D) determining a desired torque of the driver; E) calculate a control signal to the electric machine based on said weighting factor and torque desired by the driver, the electric machine being controlled according to the control signal. 4 By using the slope of the road where the vehicle is currently located, the SOC of the battery and the torque desired by the driver, intelligent choices can be made to improve the way the vehicle works. In this way, the vehicle can reduce its energy consumption, by using the battery's energy on uphill slopes, in order to then be able to charge the battery on downhill slopes. The vehicle can also get more power when it needs it most, such as on steep uphills.

Fuzzy logic is an example of a control strategy that may be used in the present invention, and which in a useful manner maps an input signal area to an output signal area area. This is done, for example, by using a list of "if-then" statements called rules. The rules themselves refer to variables and the adjectives that describe these variables. The truth content of each sentence becomes a matter of degree. Member functions are used, which can be described as a curve that defines how each point in the input signal zone is mapped to a member value, or degree of membership, between 0 and 1. However, other control strategies are also applicable together with the invention.

Preferred embodiments are described in the dependent claims and in the detailed description.

Brief Description of the accompanying Figures The invention will be described below with reference to the accompanying figures, of which: Figure 1 illustrates the driveline of a series hybrid vehicle.

Figure 2 illustrates the driveline in parallel hybrid vehicles.

Figure 3 illustrates a driveline used in the present invention.

Figure 4 illustrates the slope of the road oi.

Figure 5 illustrates the system according to an embodiment of the invention.

Figure 6 illustrates a rule base when using fuzzy logic according to an embodiment of the invention.

Figure 7 illustrates the relationship between input and output signals in a fuzzy logic controller according to an embodiment of the invention.

Figure 8 illustrates the relationship between input and output signals in a fuzzy logic controller according to another embodiment of the invention.

Figure 9 shows a circuit diagram of the method according to an embodiment of the invention.

Detailed Description of Preferred Embodiments of the Invention The invention will be described below in conjunction with a parallel hybrid system, but the invention may also be used in conjunction with other types of hybrid systems.

The driveline in a parallel hybrid vehicle is illustrated in Figure 3 and is the system in the vehicle that transfers energy from the internal combustion engine and the electric machine via the clutch, gearbox, drive axles and wheels to the road surface. The electric machine is referred to here as an electric machine, but can also be referred to as an electric machine. The internal combustion engine can be powered by diesel or gasoline, or another suitable liquid or gas. The coupling comprises a series of friction disks, which together can disengage the internal combustion engine from the rest of the driveline. The clutch can be operated by the driver via a pedal, or is automatic and a control system then maneuvers the shift and clutch. The other energy source in a parallel hybrid vehicle is the electric machine. The electric machine comprises two parts, a rotor and a stator.

The rotor is the rotating part of the electric machine and has a shaft that can either be equipped with permanent magnets or windings that will become electromagnetic when connected to an electrical energy source. In the latter case, the degree of magnetization can be controlled. The stator is the outer shell that encapsulates the electric machine and in the stator there are windings to which the energy cables are connected. When the electric machine is used as a motor, the energy from the cables induces a magnetic field in the stator. When the electric machine is used as a generator, the rotor induces a current in the stator windings which is then stored as electrical energy in the battery. As an example, the electric machine may be a 36 kW permanent magnet synchronous machine, which is a three-phase machine in which the rotor rotates synchronously with the rotating magnetic field in the stator.

A converter (not shown) is connected to the electric machine to convert AC to DC when the electric machine is used as a generator and charges the battery, and DC to AC when the battery supplies energy to the electric machine which is then used as a motor. To have a long life, the power electronics need cooling, and this can, for example, be water-based. An extreme cooling circuit may therefore need to be installed.

The battery is connected to the electrical machine and includes a number of cells connected in series to increase the voltage. The series-connected cells are then connected in parallel to increase the capacity of the entire battery pack. As an example, the batteries can be NiMH batteries, where each cell has a nominal voltage of 1.2 V. Another example of a battery is lithium-ion batteries (Li-ion), they have a better value in W / kg and Wh / kg, which makes them smaller and lighter than similar NiMH batteries.

The purpose of the gearbox and the final gear is to match the speed of the driveline on the input shaft of the gearbox with the speed of the wheels. The gear ratio in the gearbox can be varied by shifting, while the dynamics of the final gear are constant.

Figure 4 shows a system for controlling an electric machine in a hybrid vehicle according to an embodiment of the invention. The driveline of the hybrid vehicle comprises an internal combustion engine and a battery connected to said electric machine, and illustrated in Figure 3. The system comprises a tilt unit for determining the inclination of the road ot when driving the vehicle and generating a tilt signal L depending thereon, a charging unit for determining the state of charge of the battery SOC and generate a SOC signal S depending thereon, as well as a reading unit adapted to determine a desired torque by the driver, and to generate a torque signal M dependent thereon. The system further includes a controller adapted to use the slope signal and the SOC signal as inputs to calculate a weighting factor and generate a weighting signal ß depending thereon; and a control unit which is adapted to calculate a control signal Y for the electric machine based on the weighting signal ß and the torque signal M. The electric machine is then controlled according to the control signal Y.

In this way a system is achieved for controlling the electric machine, so that the stored energy of the battery can be used when it is needed most, i.e. when the road slopes upwards.

The weighting signal ß thus describes how much energy is to be taken from the battery at the current road slope and the current SOC. The control unit then generates a control signal Y to the electric machine, which indicates how much energy is to be taken from the battery when the driver desires a certain torque M. Preferably, the controller is adapted to calculate a weighting signal ß which is a non-analyzed scale factor. The weighting factor is then normalized to be a 7 value between, for example, [0 1]. According to one embodiment, the scale factor ß is multiplied by a predetermined value for the maximum torque that the electric machine can give. If e.g. the maximum torque is 300 Nm and the scale factor is 0.6, it is passed on via the control signal Y that the electric machine should lay out 300-0.6 = l 80 Nm on the driveline. The control unit ensures that the desired torque M from the driver is not exceeded. Any remaining torque required to provide the torque desired by the driver to the driveline is then taken from the internal combustion engine.

The inclination of the road u is illustrated in Figure 5 and according to one embodiment the inclination unit comprises sensors in the vehicle for determining the inclination of the road a. In this way the instantaneous inclination of the road can be determined continuously. According to a further embodiment, the derivative of the road slope is analyzed, and based on the analysis it is predicted what the future slope of the road will look like, which is included in the calculations in the controller and / or control unit to obtain a control signal for the electric machine.

Signals used in the system are preferably sent via CAN in the vehicle. CAN (Controller Area Network) denotes a serial bus system, specially developed for use in vehicles. The CAN data bus provides the opportunity for digital data exchange between sensors, control components, actuators, controllers, etc. and ensures that styr your controllers can access the signals from a specific sensor, to use these for controlling their connected components.

The charge state, SOC, is a ratio between the current charge level and the maximum charge level. The state of charge is calculated using the following formula: l soc = socím., - j z (z) df, (1) IIl fl X where Qmax is the maximum charge capacity of the battery, SOCinit is the initial value of the state of charge and i (t) is the current through the battery. The entire capacity of the battery is never used because an excessive energy cycle in the battery can seriously damage it. Therefore, there is an upper limit SOCu and a lower limit SOC] for the state of charge.

The interval between these two limits is called the SOC window.

The charge state is preferably scaled when used as an input to the controller to simplify the design by knowing that the charge state is always in the range between [0 l]. The scaling is done using the equation below: soc-soq a <2) soc, -soc, The charging unit is preferably adapted to measure the signals necessary for the above calculations, and to perform the calculations to obtain an SOC signal S.

The energy circulating in the battery is the total energy genom through the battery and is calculated as follows: Em: In J. ibm (t) in ubaz dt 1 where ibat and ubat are the current and voltage of the battery.

According to an embodiment of the invention, the controller is a rule-based controller, for example a fuzzy logic controller. Zz izzy logic uses a list of "if-then" statements called rules. By using member functions, answers can be given that are a matter of degree, not just "yes" or "no". A member function is (MF) is a curve that defines how each point in the input signal range is mapped to a membership value (or degree of membership) between 0 and 1. Two or fl your member values are given as input signals to a fuzzy operator who gives a true value as output signal . A fuzzy operator can be a logical operator such as AND, OR or NOT. Figure 6 shows an example of a rule base for the fi1 zzy logic controller. In this example, there are two member functions for tilt inputs L, "High" and "Low". For the SOC input signal S, there are two member functions, also called "High" and "Low". The output signal from the zz izzy controller also has the two member functions "High" and "Low". Figures 7 and 8 show two examples of fuzzy controllers that are graphically illustrated, where the input signals and the output signals are shown on the different axes. The surface clearly shows how the regulators work. The first regulator in Figure 7 has almost only one state, and this means a strong weighting signal ß. The strength of the weighting signal decreases slightly when the SOC decreases and when the road slope is less steep. In the system with the second controller illustrated in Figure 7, the controller is adapted to calculate a weighting signal ß to the control unit which gradually increases with increasing slope signal L and rising SOC signal S, in order to obtain an even supply of energy from the battery. The controller illustrated in Figure 8 is significantly softer than that in Figure 7, when the SOC and the road slope are large, the output signal ß is close to the maximum value. However, the support from the electric machine comes when the road slope is relatively steep. For smaller slopes, the SOC must be relatively high for the controller to react. By regulating the electric motor in this way, fuel consumption can be significantly reduced.

The system is thus preferably adapted to calculate a control signal to the electric machine to use energy from the battery when the battery SOC is in the interval between SOCmin and SOCmaX fi and the slope of the road oi indicates uphill. In this way, the vehicle gets extra energy when it needs it most, namely on uphill slopes. A prerequisite for using energy from the battery is that there is SOC between the limit values described above. However, other control strategies are also conceivable, and fuzzy-logic is only described as an example.

Preferably, the system is adapted to regenerate braking energy to the battery as the slope of the road oi indicates downhill. The vehicle is then on its way down a hill, and by taking advantage of the kinetic energy that the vehicle provides, the battery can be charged. When the speed needs to be reduced, this is usually done with a hydraulic deceleration unit, the exhaust brake and / or the wheel brakes in combination with the electric machine. As long as the battery is allowed to charge, ie as long as the SOCu has not been exceeded, and the vehicle needs to be braked, the electric machine is used as a generator as much as possible.

The invention also relates to a method for controlling an electric machine in a hybrid vehicle whose driveline comprises an internal combustion engine and a battery connected to said electric machine. The method will now be described with reference to the fate diagram in Figure 9.

Accordingly, the method comprises: A) determining the inclination of the road ot when driving the vehicle, B) determining the state of charge of the battery (SOC); C) use the slope of the road and the SOC of the battery as inputs to a controller to calculate a weighting factor; D) determine a desired torque by the driver and E) calculate a control signal to the electric machine based on said weighting factor and torque desired by the driver, the electric machine being controlled according to the control signal. Through the described method, the combustion engine can get more energy from the battery when the road is steep and SOC is sufficient.

According to one embodiment, a rule-based controller, for example a fuzzy logic controller, may be used in step C). In this way, control values for reducing fuel consumption can be calculated for the electric machine in a way that does not consume as much calculation capacity.

By using a regulator by means of which the control signal in step D) is calculated to increase gradually, an even supply of energy from the battery can be used to drive the vehicle.

Preferably, in step C), the weighting factor is calculated to be a normalized scale factor. In this way, a value can be obtained between [0 1] which can be used in a simple way to calculate how much contribution is to be used from the batteries.

The slope of the road ot is determined according to an embodiment with the help of sensors in the vehicle. In this way, the current road slope can be determined at all times.

Preferably, the control signal in step D) is calculated so that energy is given from the battery when the battery SOC is in the interval between SOCmin and SOCmaX fi and the slope of the road ot indicates uphill. Thus, energy is taken from the battery when there is available energy and when the vehicle needs extra energy on uphill slopes.

According to one embodiment, in step D) the weighting factor for the control unit is calculated to gradually increase with increasing slope and rising SOC, in order to obtain an even supply of energy from the battery. In this way, a smoother extraction of the energy in the battery is achieved, which results in less wear on this part, which in many cases is one of the most expensive components in the vehicle. ll Preferably, braking energy is regenerated to the battery as the slope of the road ot indicates downhill. Down there, the kinetic energy that the vehicle gets on a downhill slope is used instead of just braking away.

The invention also comprises a computer program product, comprising computer program instructions for causing a computer system in a vehicle to perform the steps according to the method, when the computer program instructions are run on said computer system.

According to one embodiment, the computer program instructions are stored on a medium readable by a computer system.

The present invention is not limited to the embodiments described above.

Various alternatives, modifications and equivalents can be used. Therefore, the above-mentioned embodiments do not limit the scope of the invention, which is defined by the appended claims.

Claims (16)

10 15 20 25 30 12 Patent claims A system for controlling an electric machine in a hybrid vehicle whose driveline comprises an internal combustion engine and a battery connected to said electric machine, characterized in that the system comprises: - a tilting unit for determining the slope of the road ot when driving the vehicle and generating a inclined signal (L) depending thereon, a charging unit for determining the state of charge of the battery (SOC) and generating an SOC signal (S) depending thereon; a controller adapted to use the slope signal and the SOC signal as input signals to calculate a weighting factor and a weighting signal (ß) depending thereon; a reading unit adapted to determine a desired torque of the driver, and to generate a torque signal (M) independently thereof; a control unit which is adapted to calculate a control signal (Y) for the electrical machine based on the weighting signal (ß) and the torque signal (M), the electrical machine being controlled according to the control signal (Y). A system according to claim 1, in which the controller is adapted to calculate a weighting signal (ß) which is a norinalized scale factor. A system according to claim 1 or 2, in which the controller is a rule-based controller, for example a fuzzy logic controller. A system according to any one of claims 1 to 3, in which the system is adapted to calculate a control signal to the electric machine to use energy from the battery when the SOC of the battery is in the interval between SOCmin and SOCmaXO. A system according to any one of claims 1 to 4, in which the controller is adapted to calculate a weighting signal (ß) to the control unit which gradually increases with increasing slope signal (L) and rising SOC signal (S), in order to obtain an even supply of energy from the battery. 10 15 20 25 30 13 A system according to any one of claims 1 to 4, in which the inclination unit comprises sensors in the vehicle for determining the inclination of the road ot. A system according to any one of claims 1 to 6, in which the system is adapted to regenerate braking energy to the battery when the slope of the road indicates a downhill slope. A method of controlling an electric machine in a hybrid vehicle whose driveline comprises an internal combustion engine and a battery connected to said electric machine, characterized in that the method comprises: A) determining the inclination (ot) of the road when driving the vehicle, B) determining battery charge status (SOC); C) use the slope (ot) of the road and the SOC of the battery as input signals to a controller to calculate a weighting factor; D) determine a desired torque of the driver; E) calculate a control signal to that electric machine based on said weighting factor and torque desired by the driver, wherein that electric machine is controlled according to the control signal. A method according to claim 8, in which a weighting factor which is a normalized scale factor is calculated in step C). Method according to claim 8 or 9, in which a rule-based controller, for example a fuzzy logic controller, is used in step C). Method according to any one of claims 8 to 10, in which the control signal in step D) is calculated so that energy from the battery is used when the SOC of the battery is in the interval between SOCmin and SOCmaX, and the slope of the road ot indicates uphill. Method according to one of Claims 8 to 11, in which the weighting factor to the control unit in step D) is calculated to increase gradually with increasing slope and rising SOC, in order to obtain an even supply of energy from the battery. 10 14 Method according to one of Claims 8 to 12, in which the inclination (ot) of the road is determined by means of sensors in the vehicle. A method according to any one of claims 8 to 13, in which braking energy is regenerated to the battery when the slope of the road ot indicates downhill. A computer program product, comprising computer program instructions for causing a computer system in a vehicle to perform the steps of the method according to any one of claims 8 to 14, when the computer program instructions are run on said computer system. The computer program product of claim 15, wherein the computer program instructions are stored on a computer system readable medium.